1. Field of the Invention
The present invention relates to a liquid phase growth method and a liquid phase growth apparatus, specifically to a liquid phase growth method and a liquid phase growth apparatus for forming substrates which can be used for producing semiconductor devices, in particular, such as solar cells and optical sensors.
2. Related Background Art
As the global warming is becoming more serious, there has arisen a movement to limit CO2 emissions worldwide. And attention is now being directed to the solar cell power generation which emits no CO2 at the time of power generation.
Crystal silicon-based solar cells utilizing single-crystalline or polycrystalline silicon are high in photoelectric conversion efficiency and low in degradation, as compared with amorphous Si-based solar cells, but have the disadvantage of high production costs. In order to reduce such costs, in recent years attempts have been carried out to make thin a crystalline portion of silicon which is to be a power generating layer.
The crystalline Si-based solar cell made in a thin film state can withstand a certain bend; therefore, the shape of the solar cell as a product can be freely selected to some extent, and in some cases, the solar cell can be adhered to a curved surface.
One of the methods for forming single- or polycrystalline Si which is to be a power generating layer of solar cells is the liquid phase growth method. The liquid phase growth method does not waste raw materials and allows obtaining a thin film having a necessary thickness as a power generating layer inexpensively, as compared with a vapor phase growth. Therefore, in order to improve the mass production of the thin films, there have been demands for a liquid phase growth method and an apparatus therefore which make it possible to treat a plurality of substrates together.
As a concrete example of the methods for treating a plurality of substrates together, Japanese Patent Application Laid-Open No. 1-72988 discloses a liquid phase growth method for treating a plurality of substrates together. A state in which this liquid phase growth method is carried out is shown in FIGS. 1A and 1B. In FIGS. 1A and 1B, reference numeral 101 denotes a substrate holder, numeral 102 a graphite container, numeral 103 a solution, and numeral 104 substrates.
FIG. 1A shows a state in which the substrates 104 are arranged horizontally to the solution surface and FIG. 1B a state in which the substrates 104 are arranged perpendicularly to the solution surface. In this treatment apparatus, a semiconductor layer is formed on each of the substrate 104 by dipping the substrate in the solution 103 stored in the graphite container 102.
Similarly, Japanese Patent Application Laid-Open No. 5-330984 discloses a liquid phase growth method, in which a plurality of substrates are arranged horizontally to the solution surface and a dipping process is adopted, and a holder used in the method.
The configuration of the liquid phase growth apparatus is shown in FIGS. 2 and 3. In FIG. 2, reference numeral 201 denotes a vertical barrel type reactor core, numeral 203 a crucible, numeral 204 a heater, numeral 103 a solution, numeral 104 growing substrates, numeral 209 a substrate holder, and numeral 220 a holding rod. FIG. 3 shows a substrate holder, in which reference numeral 210 denotes an attaching frame, numeral 215 a holding frame, numeral 216 side-legs, numeral 216a slotted holes, numeral 218b engaging pins, numeral 217 a bottom plate, and numeral 218 spacers.
A plurality of substrates 104 for growth which are held by each spacer can be housed in the holder. And as seen from FIG. 2, the substrates 104 for growth are held horizontally to the surface of the solution 103.
Japanese Patent Application Laid-Open No. 5-330979 discloses a liquid phase growth method, in which a plurality of substrates are arranged perpendicularly to the solution surface and a dipping process is adopted, and a holder used in the method. The configuration of the liquid phase growth apparatus is shown in FIG. 4. In FIG. 4, reference numeral 310 denotes an electric furnace, numeral 203 a crucible, numeral 103 a solution, numeral 312 substrates for growth which can be attached to a holding rod, numeral 315 a holding rod, numeral 317 a driving means, numeral 318 a holder, and numeral 319 a lifter.
The substrates 312 are held perpendicularly to the solution surface, and at the time of lowering the holding rod 315, the substrates are dipped in the solution 103 to start crystal growth.
In the liquid phase growth methods disclosed in Japanese Patent Application Laid-Open No. 1-72988 and Japanese Patent Application Laid-Open No. 5-330984, at the time of holding the substrates horizontally to the solution surface, since the solution depths of the dipped substrates are different from each other, the growth conditions of the substrates vary from each other, thereby giving rise to a problem of non-uniformness in crystal film thickness among the substrates.
On the other hand, like the liquid phase growth method disclosed in Japanese Patent Application Laid-Open No. 5-330979, when holding the substrates perpendicularly to the solution surface and rotating the substrate in the plane thereof, fluctuations in film thickness are decreased; however, since the substrates themselves are fixed to the holding rod in such a manner that the rod penetrates through the substrate, they are required to have a hole drilled therein, which means the drilled portions cannot be used for crystal growth. Further, since each substrate rotates on its center in a predetermined position, there arises a problem of limiting the supply of the solution to the substrate surface, thereby not making it possible to speed up the film deposition. And furthermore, the substrate arrangement of the prior art makes it difficult to treat many substrates together.